There has been proposed a semiconductor dynamic quantity sensor having a movable portion that is displaced in a predetermined direction according to an applied dynamic quantity. In the semiconductor dynamic quantity sensor, a semiconductor layer is located on a semiconductor substrate through an insulation layer. A trench reaching the insulation layer is formed in the semiconductor layer to form the movable portion. The insulation layer directly below the movable portion is removed through the trench so that the movable portion can be movable.
In semiconductor dynamic quantity sensors disclosed in JP-2008-264902 and U.S. Pat. No. 6,065,341 corresponding to JP-11-230986, a projection is formed directly below the movable portion. The projection serves to prevent the movable portion from sticking to the semiconductor substrate, and also serves as a stopper for limiting movement of the movable in a thickness direction of the semiconductor substrate upon application of an excessive external force.
In JP-2008-264902, a top layer (i.e., semiconductor layer) of a silicon on insulator (SOI) substrate is divided by a trench into multiple portions including a movable portion. A middle layer (i.e., insulation layer) of the SOI substrate is etched through the trench to form a projection directly below the movable portion. The projection projects toward the movable portion and is spaced from the movable portion by a predetermined distance in a thickness direction of the substrate.
In U.S. Pat. No. 6,065,341, an electrode pattern (i.e., lower wiring portion) is formed on a substrate (i.e., semiconductor substrate) and electrically connected to a movable portion through a first anchor. The electrode pattern partially projects directly below the movable portion. The projecting portion and a silicon nitride layer on the electrode pattern form a projection.
In JP-2008-264902, the insulation layer is etched through the trench in the semiconductor layer so that the insulation layer can have the projection. Therefore, manufacturing variation in the distance between the projection and the movable portion is likely to occur.
In U.S. Pat. No. 6,065,341, after the movable portion is formed in a monocrystalline silicon substrate (i.e., semiconductor layer) by forming the trench, an etching of a silicon oxide layer is performed through the trench by using the silicon nitride layer as a stopper. Thus, the silicon oxide layer directly below the movable portion is removed so that the movable portion can be movable. This approach may reduce manufacturing variation in the distance between the projection and the movable portion.
In U.S. Pat. No. 6,065,341, the electrode pattern is formed as follows. After a recess is formed in a silicon oxide layer on the semiconductor layer, a silicon nitride layer as a etching stopper and a polysilicon thin layer are deposited. Then, the polysilicon thin layer is doped with impurities and patterned into the electrode pattern.
That is, the method of U.S. Pat. No. 6,065,341 requires a process of forming the recess in addition to a process of pattering the electrode pattern. Further, after the electrode pattern is formed, a silicon oxide layer, a silicon nitride layer, and a polysilicon thin layer are formed to cover the electrode pattern. Then, another monocrystalline silicon substrate is bonded to a surface of the polysilicon thin layer. Then, the semiconductor layer is polished to a predetermined thickness. In this way, complex processes are performed to form the projection before forming the trench in the semiconductor layer. Accordingly, manufacturing cost may be increased.
U.S. Pat. No. 6,065,341 discloses a capacitive acceleration sensor as a semiconductor dynamic quantity sensor. For example, one movable electrode (i.e., beam) is provided with multiple projections, and the width of the projection is less than the width of the movable electrode. Since the width of the movable electrode is of the order of micrometers, it is difficult to accurately form the projection directly below the movable portion. Accordingly, manufacturing cost may be increased or manufacturing variation in a position of the projection with respect to the movable portion may be likely to occur.